“Imagine there’s no countries,” John Lennon sang in that dreamy anthem that gets people all wistful about world peace. “It isn’t hard to do. Nothing to kill or die for, and no religion, too.”

Eighteen years before Lennon recorded those lyrics, the science-fiction writer Arthur C. Clarke had imagined those very things, only he had gone considerably deeper than the starry-eyed Lennon. He did it in a novel called “Childhood’s End,” a touchstone work in his career and in the genre. Clarke’s vision is well served by a three-part adaptation that begins on Monday night on Syfy.

The story has been tweaked, as all novels must be when turned into television, and it’s been brought into the present (Clarke’s jumping-off point was the Cold War space race), but the depth and ambition are still there. As it opens, Earth is visited by an armada from space, with the aliens parking giant ships over the planet’s capital cities. But this is no hostile invasion, at least from appearances: The visitors get humanity’s attention by doing things like gently lowering airplanes from the sky and sending trusted deceased loved ones to explain to the living what’s going on.

It’s a delicious opening, reminiscent of the early moments of “Under the Dome,” with cool special effects and characters who are forced to process something far outside their realm of experience. One of these is Ricky — played, weirdly, by Mike Vogel, a major cast member in “Under the Dome” — who is an ordinary Midwestern guy chosen by the visitors as a go-between.

Ricky meets with the supervising alien, Karellen (Charles Dance), and becomes his spokesman. Why won’t Karellen appear directly to humans? Because, as is obvious when he finally does appear, the visitors need to build up good will with Earthlings before showing their rather off-putting selves.

By Part 2 (which begins with a version of “Imagine” on the soundtrack), the visitors have ended all of Earth’s wars, poverty and injustice. Utopia, though, leaves humans bored and uncreative; some want their old lives back.

But Clarke, who died in 2008, didn’t stop there, and he wasn’t interested in a gotcha story like “To Serve Man.” (“It’s a cookbook!”) His epic, which extends over several generations, is ultimately about the idea that humans might evolve beyond themselves, and shift to a mode of existence that makes people and Earth itself obsolete.

It’s heady, unsettling stuff, adapted by Matthew Graham and brought to life with affecting performances, especially by Osy Ikhile as a scientist who becomes the final witness to the great transition.